Gear



-June 24,- 1930.r E. WILDHABER GEAR Filed March 10. 1928 2 Sheets-Sheet 1 lNvNToR.

.lun'e 24, 1930.- E.- wlLDHABER GEAR I v Filed March 1o. 192e 2 sheets-snapt 2 INVENTOR Patented June 24, 1930 i' i UNITED-ff sirAf-rs rran'rf OFFICE Awrm)irniziaiafor BROQKLYN; New YonK i GEAR- 'A o i i Applicain meaivrarch 1o, i928. seminaaeoyzss.

The present invention relates to the tooth piementary racks which are basic to two shape of gears having teeth inclined to the gears ofa pair of gears respectively. straightgeneratricesof thei'rpitch surfaces, Fig. 7 and Fig. 8 are partial views of and more specifically to'gears having helical other, basic racks of a character in accord` 5 teeth, such as helicall gears and herring ance with the present invention. bone gears. 'o Fig. 9 is a plan view of a rack, showing One object of the present invention is to.V somewhat diagrammatically the lines vof rovide a novel tooth form for helical andV Contact between a pair of gears formed in erringbone gears, which has ay large load accordance with the present invention, or carryingcapacity and which favors eicient also the lines of contactloetween a ygear and 6o lubrication. said rack.

Another object is to provide a novel tooth Fig. 10 is a normalsection through a pair o form, which is advantageouson gears hav- "of complementary `basic racks, taken along ing teeth inclined to Athe'straight generalines 2%2 of Fig. 9.v

l5 trices of their pitch surfaces, and which. can. Fig-ll S afrOHt View 0f a rack tooth and I. 65

be eiiiciently and accurately produced. v a section along lines 3-3 of Fig; 9. V

Av further aim is to devise wholly con- In the Figuresland 2',.t he numeral 1 1L veX and wholly concavemating tooth prodenotes a pinion containing helical 'teeth f files, 'which approximate in some respects 12, which mesh -with teeth 13 of a gear 111.V the advantages obtained'with'the profiles of 'In the 'instance illustrated the gearsfll and 70 the character described in `my Patent N o. 114 have parallel axes and mesh in a man-- 1,601,750, issued OctoberV 5,1926, and which nerA that their pitch surfaces 15, 16 roll can be applied .also to gears' of narrower 'upon each other without sliding.

face.4 The tooth shape of thegears 11 and 14 Other obj'eetswill appear inthe course Iwill nowbe explainedwith reference to Fig-175 y of the specification and f-rom recital of the 3 and Fig. L It can be most readily de'- i appended Claims, J finedthrough its relation withl a basic rack, The invention is illustrated by way of eX- nl??? 1S @0 Sly l Padi 17. (S28 F122. t) Suited amples'V in the accompanying drawings, in t0 meshwlth a gear (14) Whlle its Pitch which: i Fig. 1 is apen View of a helical pinion face. 16) 0f Sld gell"- .n @preferred @H- constructedin acco-rdancewwithithe present ggml'ntcs,ilsPnogg 62215115 mventlon the Outhne of; a mamng gear b?- in a normal section, thatis to say in a plane mgfldlgctted l? dotttei btes' 1 section laid at right angles to the direction 8 5 le' als a ron e eva lona VleW Corre* of its teeth. The centers 20 of said pro- I -iiles are disposed outside of the pitchplane"v s on'dinof to Fi 1 with one Gear shown p C! g C 1n part only. 18, on a line 2l. Flg- 31S @Il enlalgedrand Daftlal VleW 0f Numeral 22 denotes the pitch point of the 4o intermeshinggear teeth, in a normal section Shown normal Section, .see also Fig.-1`.` The 90 along lilies 1 1 of Fig. T, f j line ofaction between rack 17 and 'gear 141" Fig. 4 is an `enlarged and `partial view is known to be the same as between the gears of a basicrack .corresponding to the gear 11 and 14 and can be determined in known profiles shown in Fig. 3. Fig. 4L can also manner by drawing the tooth normals (24) be considered as a normal section of a basic in any point (26) of a rack profile v19, and rack.k by determining the intersection point (28) F ig. 5 is a partial view of another basic between 'said normal and the ypitch line 18 rack, illustrative of amodiiied Vline of acof the normal section. Points "(30) of the` line of action are then obtained by dis- Lil" tion.

plane 18 rolls on the cylindrical pitch 'surj- SO i Fig.l 6 is apartialview of'npair of com-Y Aplacing a point (26) of the rack profile in 100 i L with the line of action.

3 ing gear proiiles 35, 36

the direction of the pitch line 18 a dist-ance equal to the distance between the above said intersection point (28) and 22. Any point (26) of the rack profile makes namely contact in a position (30) in which the profile perpendicular (24) passes through the pitch point 22.

In this known manner a line 32 is determined as the line the line of action between 14 are obtained by rdrawing' the outside lines 33,34 of said gears, indicated in dotted lines, and by locating` their The said end points 27, 30 of the lnie of action correspond to points 27, 26 of the rack proiile 19. The portion 26-27 of the rack profile is suited to make contact with both gears 11 and 14 and is frequently called the active proiile. Y lVhen the profile 19 is a circular arc centered outside of the pitch plane 18, in accordance with a preferred embodiment of the present invention, then the correspond- (Fig. 3) are lines other than circular arcs, that is to say lines of changing curvature. Usually the gear or larger member of a pair of gears is provided with activey tooth profiles 27--26 which are wholly concave, and the pinion or smaller member of said pair is provided with active tooth profiles 274-26 which areV both proiles having a vchangso that the vcurvature radii of arproiile have a differ- Wholly convex, ing curvature, in different points ent length.

rlhe line of action 32 of Fig. 3 has the shape already determined in Fig. 4. As is well known, the perpendiculars in corresponding pointsof conjugate tooth profiles intersect the respective pitch circles at equal distance from the pitch point. For instance the perpendiculars 37, 38 of the corresponding points 26, 26 of the profiles 35, 36 intersect the respective pitch circles V16, 15 in'points 39, V40 which have an equal distance from the pitch Vpoint 22. l-ereb y the said distances are understood to be measured Vwhich equals the corresponding distanceV lines, can therefore beconveniently be directly applied to gears on the'circular arcs the respective pitch circles. Moreover the kperpendicular 24 of the corresponding point 26 of the rack profile 19 intersects the pitch line 18 in a point 28, which has also the same distance from pitch point 22. Further it is known that the' perpen'diculars in any two points (27,

26) of the gear profile 35 intersect the pitch circle (16) inside of a distance 39-22 40-22 on pinion 11 and the corresponding distance 28-22 of the rack 17.

n Such characteristics, as distances at which tooth perpendiculars intersect the pitch analyzed to a basic raclnhnd can then without change.

withA reference the pitch point of action of the considered Y normal section. VThe end points 2l, 30 thc gears 11 and intersectionY points y V from point 45 The same holds true for the shape and position of the line of action, as is Well known. For such reasons the description will be confined to'basic racks in the following, and it is understood that racks are described particularly for vdefining gears and gear pairs. y

Referring to Fig'.v 4,"` the perpendiculars of the active vportion 26-27 of profile 19 intersect the pitch line 18 inside of a. distance 28--22 which isjsinaller than the pitch 42 of the Yconsidered normal section. Frequently the said distance (28-22) is made smaller even than one half of the pitch, as indicated in Fig. 4.

As a result tooth Contact may be made to Atravel comparatively fast over the considered tooth profileof a normal section. VFor comparison a straight rack profile 43 will be considered, which corresponds to gear teeth of involute form, as'Y known. Rack kproiile 43 is indicated in dotted lines and contacts 19, equally distant from point 44. Their perpendiculars 47, 48 intersect the pitch line 18 in two points 49, 50 which are separated of which the first one is more than double the second one. i, Inasinuch as tooth contact is made when the corresponding points 45,

50, 49 coincide with the pitch ,point 22, it is seen that tooth contact travels or passes over' a tooth profile 19, from 46 to 44, more than twice as fast as over a straight prole 43. This feature has lbeen found to effectively increase the intimacy of tooth contact of gears derived from a basic rack 17, and is for this reason 'very desirable'on gears provided withl helical teeth and broadlyl on gearsY containing teeth vinclined to the straight generatrics of the respective pitch surfaces. Helical gears l do not depend solely on the tooth profile tinuous uniform motion, uniform motion also from They are 'therefore suited to makel full use but may derive intersects ,n Other points 46 g are assumed on the two rack profiles 43 andV by distances 49-45, 50445..;1.

for effecting conthe tooth helices. y

llO

of an advantage, namely intimacy of tooth.

contact, which isdenied to spur gearsV having teeth extending in the direction of the gear axis.Y should be yprovided with Vtooth profiles of such shape that their action lasts longerV than one pitch, that is tosay thatthe point of contact travels at a moderate rate over a tooth profile, so that said travel lasts long enough to continue until a subsequent tooth enters engagement. Spur gears straight teeth parallelto the gear aXis for The latter gears, as well known,V

having` this reason contain active tooth Vprofiles Whose perpendiculars intersect the pitch surface in a distance which is at least as viding a gradual g. tween said tooth -f pitch point 22.

The gears constructed iny..accordan ce Withythe present*invention'ditfer from the gears claimed'in my Patent N o. .1,601,750 by pro-y tooth engagement r,between theprofiles of a t gearsyif fully conjugate, Aprovide .simultaneous yengagement vof matingtooth.l profiles,

that/iste say thel contactdoes'not start'on one end .of the .tooth profiles, but thefwhole active length .of said profiles comes intocontact at once. of action., There is -no pointl contactbef profiles, Which point contact moves in relation with Athevturning angles of the gears. .y

Grearsv constructed in accordance With the present invention contain` aline Vofaction and its characteristic yshape Willbe further described hereafter... v

A further difference lesides inthevfeature thatr according tothe present invention the tooth profiles have a changing curyature,y whereas the theoretical tooth prolesaccording to the formerinvention referred to are circulararcs, or approximately circular arcs.; the/gear.l or larger In both inventions member .of a pair ofgears 1s preferably pro*- .r vided With ajwholly concaye active tooth profile, and in either caseLthe gears. can be produced with simple tools methods of production. i

The gears constructedy according .to the present invention ldiffer from other gears having helicalteet-h of known enveloping type through their of tooth proliles of the shape vof the. Ishape ofthe line y, simple shape of thebasic racks andby. per-- mitting' simple, of production, scribed.

lineof contact and ,the

as Will be moreV fully de- The above said points ofvdiffer'ence may occur either in combination or .individually.

The rack l profiles ,preferably have E l a radius and are so positioned :relativelyto pitch line 18, that the, line of action l32 is.

l tangent to a straightline 52 which is per.-y

pendicular to pitch line 18. .In Fig.` 3 the line of action 32 is tangent to alinel 52 Which is parallel to a radius` '53 of the pitchcircle 15 (01'16), said radius 4passing throughthe Moreover itis also seen thaty line of action 32is also tangent to af radius.

54 ofthepitch circlev 1,5.of the shownnon.

mal section. .The .said tangents. are a meas... ure of the inclination of. theylineoffaction i..

ofthe intimacy gof tooth con` and indirectly tact.

modified form of. tooth, @derive'd'gA also from a basic rack having circulartooth-promesa. The center 55 of the. circularraclnprofile; 56

3 andnearer to the` the, .f

Y y vstarts-ati thepitch point22. j. In contradisQf normal. section. 'llhel'latter ,to tooth normal 62 vIn this case thereris-no linei.

embodying one 66v of .thej rack .The A.theoretical and Iwith efficient short durafiOn of Contact" a nQrmal section, through accurate and. eliicient .means y the.

.a hob plane 68 instead of the pitch plane 66. l

is located. again .outside .of tthe .pitch line Z f .OrtnerE Mamme...

tooth. bottoms 58,thanf-5in flhe active rack. pro,-

file isincluded betweenA the pointsh. @Candi Y 0f lMilioni 6l which' tinction. with known.. Aforms of.. enveloping files, the. line of-faction .61 passes through `pitch point .22 in a? direction'inclined-to the A. pitchr'l'ine. 57;, namely.y in a direction*v parallel, of point 59, as gvvillgb'e understood by Tthose familiarwith gearing.

teeth. deriyedjfrom. non-circular. rack ,pro-.f

Point'59 is situatedon the,pitch .line,57-, as.

shovvnj In v the Vsaidfknovvn J enveloping forms ofI te eth.,thje lineotfgaction .is

se Y tangent tothe "pitch line; 57jat thepitch point 22..-

Fig. ..6 illustrates Aa pair of .eomplementaryA tracks havingcircular tooth .profiles `63. @ne

gear of a pair of gears may beederived.fromvv a basic rackefe, and the 'other gearzofsaid pairjfromy abasic rackT 65. Generation of a gear maybe..elfected by providing atool.

O f said raclrs .and ,byefecting suchmotion betweenA said tool and ya gear v. blank, as. exists i when l. the, pitch Y plane in.y mutual contact.

been omitted 1n the .Figures 4 and 5,..for

Moreover. no .shading has been lapplied to the normal; sections for the same reason,.namely .for clarifying the explanatory of action, through H.the

lines. 1 conjugate to rolls: Without slidingonthe l cylindrical pitch surfaceof the gear blank. profiles of. theftwo racks are entirelycomplementaryvand .their pitchq.; planes. (66). coincide when .the protilesof; Esaid racksfare vcount of the equal. form offthefproilelines. vofthe :two complementary racks, reference (63) is by. 1

providing hobs having multi-ple threads any-d.l

by operating. said hobs infaccordance withy general`- disclosureyof .my Patent No. 1,653,686 issued December 27, 1927. v Thethreadsurfaces ofv a hob-may .be determined in known manner .as if they were tooth surfaces of a helical-pinion. Whose thread is conjugate to a .rack 6l or a` rack.' 65..,and suited .to `be enveloped bythe tooth sides ofsaid rack,contains a'threa-d profile 'different from a circular arc', especially When said hob is provided With multiplel threads... Naturally a circular arcis-asim-v pler line than. any othercu-rve, and capable .cfyery accurate reproduction, on .account bejshovvn hoW may beldevlised, `Whose thread is conof its simplicity. lIt will now Jugate to arack of theY character shown in.l

Fig. 6, andwhich nevertheless contains the-` Y 1... Y oreticalfly.; accurate circulargp'rofiles- In Fig. 5 I have indicateda somewhat;V

A truly i circular thread. profile may be .i

.hob meshes` With f a .rack

llf)

-, ion, or gear,-

Plane 68 namely contains the centers of the i circular'tooth profiles 63 of a normal sec'- tion of the rack teeth, and for this reason the rack may reproduce its own circular profile on any hob, worm, pinion, or gear which meshes. with said rack in a manner, plane 68k of the rack canVbe considered as rollin without sliding on cylin plained Vin* my referred to. Y

The rack embodied by a hob meshes-then in aldifl'erent manner with said hob and with Y cific embodiments will now 1 action,

a gear blank. It rmeshes with ai gear blank in the manner corresponding to a pitch plane 66 of the rack, while it meshes with l an involute of a circ1e,having a base circle 1 '73. 74 denotes a per endicular to the profile 70, and is seen to e tangent to base circle 7 3. An involute of a circle is known to be next to a circle in simplicity.

The profile 75, Fig. s, of the racks 76,177Y

is also an involute, having however its base circle 78 differentl positioned with respect to pitch line 79. t is seen yto be a circular arc crossing pitch line 79. A perpendicular to profile 75 is shown at 80. v

Thus far specific embodiments of myv in'- vention have been disclosed. A more general embodiment will now bev described with reference to the Figures 9, 10 and 11.

This general embodiment and former speacterized through the aspect of a line of simultaneous contact between a pair of gears, and further through their lines of action. The said line of contact, the line of and the tooth shape of gears'are interrelated in known manner and vmay be Vdetermined one from another with theV known methods of the gear art.

In Fig,V 9, 82 are the tooth sides of a basic rack facing corner 2,-and 83 are the tooth sides of said rack facing corner Q. corresponding tooth profilesfof the basic racks are equally denoted with 82, 834 in Fig. 10. The plane containing the' `two axesfof a pair of gears is indicated as a dash and dot line 84 in Fig. 9. v The lines 85, 86 of simultaneous contact between a pair of gears are alsosituated on the tooth surface of a basic rack and extend between end points 7 88.

that the the contacting rical surface of said'hob, worm,"pi`nV This feature has been-'fully ex-g Patent No'. 1,653,686 above planes, namely plane perpendicular to the plane of the drawing plan view those skilled in the art. On the i and which permits accu-V be broadly char` pinion having convex tooth Thel It is noted that the lines of contact 85, 86 extend lengthwise ofthe teeth a distance 89 smaller than the axial pitch 90. 'This feature holds trueV for all preferred embodiments of the present invention. Moreover a line of contact-85is tangent to a plane '91 which is parallel tothe plane 84 containing the two axes of the pair of gears.

84 and plane 91 are Fig. 9, which .is parallel to the pitch plane (79), and are seen as straight lines in the Fig. 9. `In many cases a line of contact 85 is moreover tangent to a normal profile of the tooth surface, that4 is to say tangent to the'profile of a section 92 which Vis perpendicular to the kdirection of the rack teeth. In -some`cases a line of contact is moreover tangent to a plane 98, which is perpendicular Vto the axes of the gears.

The numeral 94 denotes the pitch point, and 95 the linej of action ofthe normal section Fig. 10. As has been alreadydescribed,

the tooth perpendiculars 96 intersect the pitch line 79 inside of a distance'lOl which is smaller than the pitch 97, and which is preferably kept inside of one half of said pitch. The line of action 95istangentto a line 98, which is perpendicular to pitch line 7 9, and in many cases the line of action Both is also tangent to a circle drawn with pitch s 'point 94 as the center. In Fig. 10-the said circle practically coincides with a portion ofthe tooth profile 83.'

In Fig. 1l a Contact is seen in a view taken at right angles to the tooth surface. It is a concave curve having an inclination much steeper than the straight line of contact 99 of known involute gears, shown inl dotted lines for comparison.V In the viewFig. 11 the normal profile previouslyreferred to appears as a straight line 92.

Vhen a pair of gears mesh together, and especially when motion is applied from a profiles to a gear having concave tooth profiles, the lines of contact 85, 86 move in a direction lengthg wise of the teeth, in the direction of arrow 100, Fig. 11. They maintain thereby a constantA shape and a constant distance from -to remain in the zone of contact.

line 85'of simultaneous toothV lil() lli) . than one pitch, said A 'It 's understood that furtherl modiiications may be made in my invention Without departing from'its spirit. For denition of itssco'pe 'it is relied upon the annexed claims.

l. A gear containing helical teeth suited to contact With its basic rack along lines curved in a projection to the pitch plane of said rack, the active profile of anormal section of said teeth being Wholly concave and having a changing curvature, the perpendiculars of said profile intersecting the pitch surface inside of a distance smaller than onel half of the pitch of said normal section.

2.y A gear containing teeth inclined to the straight generatrices of its pitch surface and suited plane of said rack, the active profile of a normal section of said teeth being Wholly concave and having a changing curvature, the perpendiculars of said profile intersecting the pitch surface inside of a distance smaller than one half of the pitch of said normal section.

3. A gear containing -helical teeth suited to contact With its basic rack along lines curved in a projection to the pitch plane of said rack, the profile of a normal section of said teeth having a curved line of action, and the perpendiculars of the active part of said profile intersecting the pitch surface inside of a distance smaller kthan one half of the pitch of said normal section.

4. A gear containing teeth inclined to the straight generatrices ofits pitch surface, a normal section of said teeth having a line of action corresponding to a distance smaller than one pitch, said line of action being tangent to a radius of the pitch circle of said normal section. Y

5. A gear containing helical teeth, a normal section of said teeth having a line of action corresponding to a distance vsmaller line of action being tangent to a radius of the pitch circle of said normal section. j

' 6. A gear containing teeth inclined to the straight generatrices of its pitch surface, a normal1 section of said teeth having a line of action corresponding to a distance smaller than one pitch, said linev of action being tangent to a line parallel to a radius of the pitch circle of said normal section, said radiusi passing through the pitch point of said circ e.

7. A gear containing teeth inclined to the straight generatrices of its pitch surface, a normal section of said teeth having a line of action corresponding to a distance smaller than one pitch, said line of action being tangent toY a circle centered in the pitch pointof said normal section.

8. A gear containing helical teeth of ch anging profile curvature and suited to con,-

', avitc'li, said-"line ,offaction to contact with its basic rack alongl lines curved in a projection to the pitchy tact With its basic rack along lines curved in a projectionto the pitch plane'of said rack, Vsaid rack having a whollyjconvex active tooth profile in-a/ normal section,fthe 4perjwendicular to said profile/intersecting the pitchvline of the: rack` inside -ofal distance smaller than thefpitch ofsaid normal section.r l V 'Y a Y. l n .19.,Adgea'r containing lhelical teeth suited tojmjesh With abasic rack having substantil ally y,circular tooth profiles, a normal sec- 1 tionof said teeth having aline of' action corresponding to, a distancesmaller thanone beingftangent'to a: of the pitch circle,

` line parallel to the (radius which, passes through` the pitch point'of said circle. Y 1

,10, A -gear containingn helical' teeth of changing profile curvature suited to mesh vv'ith a :basic rack having substantially circular active tooth proles, the centers of said profilesV being disposed outside ofthe pitch line of said rack, andtheperpendiculars to said tooth profiles vintersecting'the pitch line,

l of the rack inside of a distance smaller than l one half of the pitch."

ll. A

gear containing helical teeth of j AVchanging profilecurvature suited .to Vmesh ,Witha basic rackhaving active'tooth -profiles y 'offtheform' of ,single "circi'ilar-l arcs inv a normal section,`fthecenters ,being disposed` outside `of the pitch line of said rack., and the fperpendiculars tov said j'tooth profiles intersecting the pitchline'fof klthe rack inside one* half of the pitchoffsaid normal section. l2. A gear containing-teeth inclined to the direction of its axisV and'suitedto conta'ct With its Vbasic p projection to the 'pitch plane yof `saidrack, said rack having activetooth profilesof the form of single circular arcs, Ysaid gear having active tooth profiles which are Wholly7 conof 4a distance smaller "than,

rack along lines curved in a of sai-df ,profiles v cave and of changing curvature', the perpen-y diculars of the'last said profilesv intersecting the pitch surface insideof distances smaller than 'one half of 'thepitchl j 13. A'gear containing heliCal'teetlr suited to Contact Witharack a projection to the pitch plane of said rack, said rack having active tooth profiles 'of the form of singlev Acircular'arcs","'the active vprovfile'of anormal section'of lal gear tooth ybeingY 'Wholly concave andY having Y'a "changing,

curvature, Athe yperpendiculars o f, *theY last said profile intersectingthe pitch; surface inside of la distance smallerthanjone halfof the' pitch in said normal section, *l

Q14., A pair ofi gearscontainingl teethv in- 7.

clined to thestraight. generatrices oftheir respective pitch surfaces, lsaid gearsy having toothrsurfaces so relatively t0; their contact between-j r`said' `Curved line, said curved line pitch being tangent along lines curved in yshaped and so positioned. v

surfaces, that tooth -gearsjs fer'fected infra that'tooth contact between said Vfected in a line extending lengthwise of the tcetha distance smaller .than the axial pitch Vof the to a plane parallel to the plane lcontaining the axes ofsaidgears. .Y

l5. A pair of gears containing teeth inclined to the straight Igeneratrices of their 16. A pair vof gears containing helical teeth, having toothsurfaces'so shaped and so positioned relatively to their pitch surfaces, that tooth contact Y isV effected in a ,line tangent'to the proleof a normal section of said teeth, said line re# Y ceding from said; profile on either side of 'normal section. of said teeth,

v wholly concave in a view at right angles to e a tooth surface and` occupying a distancev smaller than the axial pitchvof the teeth in,`

' teeth,

' 17. Apair yof said point of tangency and occupying a distance smaller thanthe axial. pitch of said teeth inlengthwise direction of the teeth.

gears .containingV helical teeth, having tooth fected ina line tangent to the profile of a said line being lengthwise direction of the teeth. a A pair of gears Vcontaining teeth in clined to the straight genera'trices ofthe respective pitch surfaces and suited toV Vcontact with each other along `projection to the joint tangential planey of lines curved in la their pitch surfaces, vthe tooth profiles of one gear' of said pair being wholly concave and having a changing curvature, said gears having tooth surfaces so shaped and so positioned relatively to their pitch surfaces that contact between saidV gears is effected in a line extending lengthwise ofthe teeth a dise tance smaller than one half of the axial pitch of theteeth.

19,. A pair of gears Acontaining helical having tooth surfaces so shaped and so positioned relatively to their pitch surfaces teeth, said line being tangent to a plane parallel to the plane containing the axes of saidV gears 'andbeing wholly concave Vina view perpendicular toa-tooth surface.

.20. A pair of gears containing teeth inclined tothe straight generatrices of the reparallel ifi/eme? teeth, saidline being tangent to Ya l*plane of said gears a view perpen etween said gears f surfaces so shaped and so i positioned relatively to their pitch surfaces that tooth contact between said'gears is efspective pitch surfaces, said gears having tooth' surfaces so Vshaped and so positioned relatively to their pitch surfaces that Vcontact between said gears is effected in afline extending lengthwise of the teeth a distance smaller than the mean axial'pitch of the to the plane containing the axes and being wholly concave in dicular to a tooth surface.

ERNEST VILDHABER.

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